Cyber Monday deals at T-Mobile are live and if phones are on your holiday shopping list, you may want to check these deals out. Beginning from Black Friday on Nov. 23, the carrier has offered new phones either for free, or up to $750 off the phone's full price. The catch (because isn't there always one?) is that you must open up a new line of service to your plan and trade in an older, eligible phone. In some cases, the deal requires you to activate two lines of service. And if you already pay for two lines, the deals work when you add a third.

In addition, you'll be seeing these savings as bill credits, spread out over 24 or 36 months. So while you will end up saving money, it'll be over a long period of two years or more.

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If you're confused about how the bill credits work for phones that have $750 knocked off from their price tags, here's an example: Say you purchase a $900 phone and receive $250 from the phone you trade in (again, the device needs to be eligible). On top of that $250, you'll get $500 in credit across 24 or 36 billing cycles.

If you open up a new line without trading in a phone, you can get a free T-Mobile Revvl 2 (or Revvl 2 Plus for $84). Again, the discounts will be applied via monthly bill credits over the course of 24 months.

T-Mobile also has promotions for the Apple Watches, iPads and more. Again, you'll need to activate a new account with a voice line and add a line of data. Devices include: